Liquid bridge wire

ABSTRACT

AN ELECTROHYDRAULIC SYSTEM HAVING TWO ELECTRODES SPACED IN WATER AND A VERY SMALL CONDUIT THROUGH ONE ELECTRODE TO DIRECT A THIN STREAM OF CONDUCTIVE LIQUID FROM THAT ELECTRODE TO ANOTHER ELECTRODE SO THAT ANY DISCHARGE ACROSS THE ELECTRODE FOLLOWS THE PATH PROVIDED BY THE CONDUCTIVE LIQUID.

Feb. 2, 1971 GERBER 3,559,435

LIQUID BRIDGE WIRE Filed Sept. 25, 1968 3 Sheets-Sheet 1 III! --I|||| XI ig-iii if; 1} 5m \4 ii 3 ft": 6 I :1 I ""ll "'"ln J J? m 11m ||||HTANK ELECTRIC STORAGE UNIT INVENTOR HOWA RD L. GERBER ATT'Y.

H. L. GERBER LIQUID BRIDGE WIRE Feb. 2, 19711 Filed Sept. 25. 1968 3Sheets-Sheet 2 tr/ V//// INVENTOR HOWARD L. GERBER BY 4 z a m 2,, W71 H.L. GERBER 3,559,435

LIQUID BRIDGE WIRE Filed Sept. 25, 1968 I5 Sheets-Sheet 5 INVENTORHOWARD L. GERBER United States ABSTRACT OF THE DISCLOSURE Anelectrohydraulic system having two electrodes spaced in water and a verysmall conduit through one electrode to direct a thin stream ofconductive liquid from that electrode to another electrode so that anydischarge across the electrode follows the path provided by theconductive liquid.

My invention relates to an electrohydraulic spark discharge system andparticularly to an electrohydraulic spark discharge system which has aliquid bridge wire of highly conductive liquid.

Electrohydraulic forming systems of the prior art have used in manycases two electrodes having only a space therebetween and in other caseshave used a conductive bridge wire across the space to form a conductivepathway for the heavy current which passes between the electrodes toform a spark discharge. The bridge wire system is subject to thedisability that each time the system is fired the bridge wire must bereplaced. This system is very slow to operate.

Firing an electric current across two electrodes produces a non-uniformpath for the electric discharge. Because of the nonuniform path thepattern of strength generated by firings is variable. Further, thebreakdown potential necessary to start discharge across this pathvaries. Discharge through an insulating liquid requires large electricfields and a resultant short gap with short gap tolerances. This givesrise to a high rate of erosion of electrodes and a greatersusceptibility to variable gap spacing. Performance from test to testmay vary greatly because of the shortness of the gap between theelectrodes and erosion caused by repeated firing, the percentagevariance of the gap causes differences of impulse and differences ofpotential necessary to break down the gap. Because of these facts avarying amount of residual energy is available for forming.

By using an electrically conductive preferential pathway and controllingthe diameter and the type of flow in the pathway I can control themagnitude and direction of the pressure wave using a minimum ofelectrical energy to establish a highly conductive plasma in aparticular configuration. Generally, for best efiiciency the pathway isof small diameter with maximum energy density.

The breakdown in this process is not an avalanche, as in the case ofdielectric breakdown, but a plasma that grows until a critical size isachieved. After this critical size is achieved an avalanche of electronsproceeds and rapid breakdown occurs, During the time of the plasmagrowth the flowing conductor and conductor pathway determines thedischarge path. After the critical size is reached, the discharge isdetermined mainly by the elecatent 3,559,435 Patented Feb. 2, 1971 "icetric fields and photo-ionization. The fact that the plasma growthfollows the conductive solution is a primary advantage of thisconductive system. The breakdown is controlled by directing the fiow ofthe conductive fluid. If nonsymmetrical forming is required, the flowcan be appropriately directed as indicated elsewhere in the disclosure;If repetitive forming is contemplated as in can forming the saving ofelectricity and fluid are appreciable. No energy is lost as in breakingdown an insulating liquid because a conductive pathway is provided.

It is an object of this invention to provide an electrohydraulic sparkdischarge system having high efficiency and a low energy requirement forbreakdown.

It is a further object of this invention to provide an electrohydraulicsystem in which the arc discharge can be repeated at a rapid rate withuniform results.

It is a final object of my invention to provide an electricallyconductive pathway of small diameter and maximum energy density.

In brief, my invention is a can shaped pressure chamber having a thinexpansible outer membrane forming the outer shell of the chamber. Thechambers filled with water and two electrodes project into the chamber.A thin stream of highly conductive liquid is pumped through a small holein one electrode and impinges against the other electrode. When a highpotential is placed across the electrodes, current preferentiallyfollows the highly conductive stream giving a discharge of uniformstrength and shape from one electronic discharge to the next electronicdischarge.

Other objects and advantages of the present improved method andapparatus will become apparent during the following discussion of thedrawing, wherein:

FIG. 1 is a right-side elevational view partly broken away and partly insection showing an electrohydraulic forming apparatus of my invention.

FIG. 2 shows an embodiment of the electrohydraulic chamber of myinvention wherein one electrode is concentrically mounted about another.

FIG. 3 shows a schematic diagram of the synchronous electrical andhydraulic firing system.

FIG. 4 shows an embodiment of my invention with one electrode mountedabove another.

FIG. 5 shows the embodiment of my invention with one electrode mountedabove another and swirling water about the conductive path.

FIG. 6 shows a detailed view of the electrohydraulic chamber, can bodyand stylizing die of FIG. 1.

Electrohydraulic forming devices are used in various applications and myarrangement can be used in various applications but is shown here inFIG. 1 as a device for forming or stylizing a can. One type of formingapparatus 1 for a tubular material is shown here. A control panel may beprovided at the front of the apparatus to control the various steps ofthe forming operation. An energy storage unit 2 is shown to store largeamounts of electricity in capacitors. A bank of capacitors may be in thestorage unit, and power cables conduct the energy from the capacitors tothe electrodes of the die assembly.

The die assembly 3 illustrated is used for forming a can to give astylized exterior around the peripheral circumference of the can. Thedie assembly 3 has a pair of vertical split die halves 4 carried in apair of die holders 5 which are adapted for a snug fit. Inserts 6 areprovided in the die holders so that they may fit the die halves beingused in the particular application. The split die holders 5 are mountedon the frame of the apparatus for horizontal movement between a closedforming position and an open or unloading position wherein the diehalves are spaced apart from each other in a horizontal direction. Thearrangement in FIG. 1 is shown only for purposes of illustration.

The embodiment of my invention in FIG. 2 shows a channel 7 centrallylocated in the primary electrode 8 and mounted in the center of theelectrode holding stations. A durable elastomeric boot 9 is mountedabout the electrodes and sealed to form a chamber. A conductive solutionor electrolyte is pumped down through the center channel 7 of the innerelectrode 10 around the outer electrode 11 and back up into the exitconduit 12. Ordinary tap water or distilled water, as may be de sired,is pumped into the forming element through conduit 13 down into thebottom 14 of the chamber where it passes back toward the electrodestation 8 and passes out of the chamber along with the conductivesolution. In this way there is little or no contamination of the water.All channels and ports are shown oversized for ease of illustration.

If a valve 15 is inserted in the conduit 16 which feeds the conductivesolution through the center electrode 8 (FIGS. 2, 4 and 5), theconductive solution may be used as a trigger for allowing the storagecapacitor 2 to discharge electricity from one electrode to the otherelectrode. If the arrangement of the parts in the can chamber is such asto allow the conductive solution to function as a trigger then thecircuit arrangement shown in FIG. 3 may be used. The tank valve andtrigger '17 are synchronized so that shortly after the conductivesolution forms a conductive bridge between the electrodes the electriccurrent is triggered and released to pass current from one electrodethrough the conductive bridge and to the other electrode. The conductivesolution is exploded and generates force which may be used toelectrohydraulically form a workpiece into a die cavity as shown inFIG. 1. By

intermittent flowing of the conductive solution a savings of solution iseffected. However, the conductive solution may be run continuously if sodesired.

As an alternative embodiment the electrodes may be mounted one above theother and concentric to a common axis as show-11in FIG. 4. In thisembodiment the conductive solution is passed into the chamber through achannel 18 along the axis of the upper electrode 19 and passes out ofthe chamber through a channel in the lower electrode 20. Locatedradially from the channel are ports 21 for admitting water or some othernonconductive pressure transmitting liquid such as benzene or acetone.This water flows through the chamber in the same direction as theconductive solution. The conductive solution and 'water may exittogether as waste (FIG. 4) or may exit separately as shown in FIG. 2.

In FIGS. 2 and 4 the internal edges 22 of the electrodes are shown inthe rounded condition they assume after repeated arcings between theelectrodes have caused erosion of the electrodes along their inner edgenear the conductive solution. The electron current in the embodimentshown is from the lower cathode to the upper anode 19. The upperelectrode is more easily replaced and wears more rapidly due to electronimpact. In order to reduce erosion due to heat vaporization materialssuch as tungsten copper, tungsten silver, tungsten and stainless steelmay be used in the upper and lower electrodes.

The upper and lower electrode arrangement appears more attractive sincethe arc is directed vertically from one electrode to the other. In thisarrangement the force of the pressure or shock wave is primarily radial(cylin drical wave) and transmits maximum force against a can side toalter its shape. In the upper and lower electrode arrangement theconductive solution and the water move at about the same speed so thatthere is very little mixing between them.

The shaping 23 of the upper and lower ends of the electrohydrauliccompartment is designed to promote an even application of force to thesides of the can. As an optimum the length of the wave path is adjustedso that reflected waves interfere and there is a simple cancellation ofall impulses except the initial shock Wave.

In FIG. 5 the electrodes are located one above the other each having aconduit solution entrance. The principal difference between theembodiment of FIG. 5 and that of FIG. 4 is that the water is given atangential swirl by conduit 24 in the embodiment of FIG. 5. Thetangentially swirling water plus any conductive solution which has beendiffused into the tangentially swirling water is removed at a lowerpoint and carried oif as shown at a water exit port. The conductivesolution passes to the lower electrode port 25'where it is drawnoif'a'nd passed" up through one or more of the pillars 26 to aconductive solution exit port 27.

These elements of the electrohydraulic structure fit into a rubber boot28 thus forming a chamber 29. The electrohydraulic chamber 29, can body30 and stylizing die 4- are all mounted upon a can forming machine asshown in FIG. 1.

Greater detail of the electrohydraulic chamber 29, can body 30 andstylizing die 4 is shown in FIG. 6. A lifter plate 31 is underneath theentire structure and its contour is such that it fits exactly the bottomof the can being formed. Surrounding the electrohydraulic chamber 29 andthe can body 30 is a stylizing die 6. The interior of this die iscontoured to be the complement of the desired finish of the can. Veryclearly the interior of the die can be used for reshaping, reforming,fine detail embossing or changing the can body shape. This formingchamber is usually made of split dies so that the die may be readilyremoved from the can after the can has been formed. The formed can isstronger and has greater volume than the unformed can.

Considering the elements of the electrohydraulic chamber and proceedingfrom the outside, the first element of the electrohydraulic chamber isthe rubber membrane or boot 9 which surrounds and forms the outerelement of the chamber. When an electrohydraulic arc is formed the bootis pressed outward from within and pressed against the can to push thecan into the interstices of the forming die 6. The electrodes 32, 33 andtheir supporting structures 34, 35 are held a certain distance apart bysupport pillars 36 which extend from the upper electrode supportstructure 34 to the lower support structure 35. These pillars 36 may behollow so that returning electrolyte and returning water may be passedthrough them. The supporting structures about the upper and lowerelectrodes are formed in the shape of a reflector so that impulses whichcome from the are between the electrodes are refiected to the area ofthe rubber boot 9 located near the top and bottom of the can which is tobe stylized. In this way the pressure against the side of the can ismore equalized throughout than would be the case without the reflectors.If the hydraulic length of wave travel between the point of generationand the point of impact is one quarter of a wave length than the secondand subsequent waves interfere to give a net result of one wave onlyimpinging on the boot and without reverberations.

Between the electrode and the upper supporting structure is an electrodeinsulator, which may be made of a rubberized material. The electrodesare located so that the are produced between them is central in thechamber to give a constant and nearly even impact against the sides ofthe chamber each time the arc fires.

The pressure transmitting liquid may be water but if maximum pressuretransmission is desired a sorbitol or methylene chloride solution orbenzene or acetone may be used. Concentrated solutions of sorbitol ormethylene chloride produce a minimum of fifty percent (50%) moredeformation than is produced by using water as the pressure transmittingliquid.

It is understood that the liquid in the chamber may be under pressureprior to the discharge of the electrohydraulic are as set forth in theapplication titled, Apparatus for Hydraulic-Electrohydraulic Forming ofTubular Elements, by Donald J. Roth and assigned to the same assignee asthe present invention.

An advantage to the method and apparatus of the present invention isthat a lighter weight can is possible because of walls which arestrengthened by stylizing.

Another advantage is that the use of an electrolyte passing throughwater permits interior pressure to be exerted upon the chamber wallswhile the electrolyte is being jetted through the water.

A further advantage is that by circulating the solution and water in thesame direction loss of conductive solution by mixing is held to aminimum.

Another advantage is that each pressure wave is of similar shape andstrength to impart a similar result to a series of cans.

Another advantage is that higher efficiencies result because of therestriction of electric breakdown to a smaller volume with high energydensity and less energy lost in breakdown.

Another advantage is that larger gaps and gap tolerances can be usedwith a liquid electrolyte because the current flow is restricted incross section.

The final advantage is that savings of conductive fluid and electricityare effected where high speed operation with many arcings per minute isdesired.

The foregoing is a description of the illustrative embodiment of theinvention and it is applicants intention in the appended claims to coverall forms which fall within the scope of the invention.

What is claimed is:

1. An electrohydraulic device for forming tubular workpieces adapted tobe inserted into a forming die comprismg:

a chamber of elastomeric material,

a first electrically nonconductive liquid in said chamber fortransmitting a pressure wave,

electrodes mounted in said chamber and adapted for connection to anexternal power source,

means for establishing an ionized liquid preferential conductive pathwayof small diameter between said electrodes.

2. An electrohydraulic device for forming tubular workpieces as setforth in claim 1 wherein said external power source comprises:

electrical energy storage means, and

means for conducting said first liquid into and out of said chamber.

3. An electrohydraulic device for forming tubular workpieces and adaptedto be inserted into a forming die comprising:

a first electrode having a channel therethrough for passage of a fluid,a second electrode spaced from said first electrode, a chamber ofelastomeric material mounted about said electrodes and having anonconductive fluid therein,

means for forcing an electrolytic fluid through said channel and towardsaid second electrode to form a preferential conductive pathway betweensaid electrodes,

means for providing a shielding current of fluid between saidnonconductive fluid and said electrolytic fluid to avoid mutualcontamination, and for flowing a nonconductive pressure transmittingfluid into said chamber,

means for conducting the overflow of said chamber out of said chamber,and

means for connecting energy storage means across said electrodes wherebyan arc is formed when said preferential conductive pathway isestablished.

4. An electrohydraulic device as set forth in claim 3 furthercomprising:

mounting means in the top of said chamber for holding said first andsecond electrodes,

said first electrode being generally tubular in shape,

said second electrode being generally tubular and larger in diameterthan said first electrode and mounted so that its lateral surfacesgenerally surround the lateral surfaces of said first electrode, and

an insulator secured between said first and second electrodessubstantially filling the space between said first and secondelectrodes.

5. An electrohydraulic device as set forth in claim 4 in which saidshielding current means comprises:

a body mounted in the bottom of said chamber and having means fordirecting a shielding current about said electrodes whereby saidconductive fluid and said nonconductivefluid are kept separate.

6. An electrohydraulic device as set forth in claim 3 having,

first mounting means for closing the top of said chamber and supportingsaid first electrode and an insulator,

insulator means fastened between said first electrode and said mountingmeans for electrically insulating the first electrode from said mountingmeans,

said second electrode being generally tubular in shape to form a channeltherethrough and of about the same size as said first electrode wheresaid electrolytic fluid is jetted from said first electrode to saidsecond electrode and evacuated from said chamber through said secondelectrode.

7. An electrohydraulic device as set forth in claim 6 in which saidshielding current means comprises:

an annular channel formed between said mounting means and said insulatormeans,

conduit means formed in said mounting means and connecting said annularchannel to the exterior of said device.

8. An electrohydraulic device as set forth in claim 7 in which saidoverflow conducting means comprises:

a second mounting means for holding said second electrode from saidfirst mounting support means for spacing said second mounting means fromsaid first mounting means,

second conduit means in said mounting means and said support means forconducting the electrolytic liquid from said channel in said secondelectrode and conducting the fluid overflow through ports in the secondmounting means to ports at the exterior of said first mounting means.

9. An electrohydraulic device as set forth in claim 6 in which saidshielding current means comprises:

conduit means in said first mounting means for injecting a nonconductivefluid into said chamber at a bias whereby a spirally swirling shieldingcurrent is set up in said chamber.

10. An electrohydraulic device as set forth in claim 9 in which saidoverflow conducting means comprises:

a curved conduit extending from adjacent said second electrode tooutside said chamber whereby said nonconductive fluid is evacuated fromsaid chamber.

11. An electrohydraulic device as set forth in claim 10 in which:

third conduit means is connected to said second electrode channel forevacuating said electrolytic fluid from said chamber.

12. A method of pressure wave generation comprising the steps of:

jetting an electrolyte solution from one electrode to another through anonconductive liquid to form a conductive bridge,

flowing a sheet of nonconductive liquid in a plane generally adjacent toand surrounding said conductive bridge to form a shield between saidnonconductive liquid and said conductive bridge,

7 applying an electric potential across said electrodes whereby an arcis formed to generate a pressure wave.

References Cited UNITED STATES PATENTS 3,200,626 8/1965 Callender 72-563,222,902 12/1965 Brejcha et a1 72-56 8 2/ 1966 Inoue 72-56 5/1966Grove, Jr., et a1. 72-56 7/1969 Balcar et a1. 72-56 US. Cl. X.R.

